Molten metal processing

ABSTRACT

Processing apparatus and methods for introducing material into a molten metal are provided. The material is introduced through a tube, which leads into the molten metal flow between the exit from a chamber and the entry back into a chamber. Increased breaks for material injection and/or better material injection are provided as a result.

This invention concerns improvements in and relating to metalprocessing, particularly to apparatus and methods for introducing gasesand/or solids into molten metal.

At various stages during the melting, treatment, purification anddistribution of molten metals it is desirable to introduce externalmaterials into the molten metal. These may be gases to extract undesiredcomponents from the molten metal into an accompanying slag, powders tointroduce desired components into the molten metal or other materials.

Existing techniques for achieving this aim include the use of lanceswhich are dipped into the molten metal and through which the materialsare introduced. The lances are separate components from the chambercontaining the molten metal and are removed from the molten metal whennot being used. Existing techniques face a number of limitations,particularly in relation to the amount of material which cansuccessfully be delivered with time and the degree of contact providedbetween the material and the molten metal, given that the material isintroduced at a discrete location and needs to be spread throughout themolten metal.

The present invention has amongst its aims the provision of apparatusand methods for introducing materials into molten metal. The presentinvention has amongst its aims the provision of apparatus and methodsfor introducing materials into molten metal so as to provide greatercontact between the material added and the molten metal as a whole. Thepresent invention has amongst its aims the provision of apparatus andmethods for introducing materials which allow a greater range ofmaterials to be successfully introduced using the same apparatus ormethod.

According to a first aspect of the invention we provide processingapparatus for molten metal, the apparatus including a chamber for themolten metal, a molten metal mover, an inlet leading from the chamber tothe molten metal mover and an outlet leading from the molten metal moverto the chamber, a tube leading into the apparatus between the start ofthe inlet and the end of the outlet.

The processing apparatus may be for melting metal or metal containingmaterials and/or for processing molten metal and/or for purifying moltenmetal and/or for distributing molten metal at a location, the locationbeing between 10 cm before the start of the inlet and 10 cm after theend of the outlet, preferably being between the start of the inlet andthe end of the inlet. The processing apparatus may be for introducingjust a gas into a volume of already molten metal. The chamber may be acharge well, particularly in such a case. The apparatus may furtherinclude a furnace, ideally separate from the charge well. Preferably theoutlet from the charge well leads to the furnace. Preferably the inletto the charge well leads from the furnace.

The chamber may be a furnace itself.

The molten metal mover may be a pump. The pump may be a mechanical pump,but is preferably an electromagnetic pump.

The tube preferably leads into the apparatus other than within themolten metal mover, particularly the part thereof which imparts motionto the molten metal. Preferably the tube leads into the apparatusbetween the end of the molten metal mover and the end of the outlet.

The tube may be provided in a wall of the chamber. The tube preferablyleads into the apparatus at the end of the outlet.

The tube may be provided in a component around the outlet. The tubepreferably leads into the apparatus at the beginning of the outlet. Thetube preferably leads into the apparatus at the outlet from the moltenmetal mover.

The tube may lead to a location at which molten metal is provided inuse, a gas permeable element being provided between the end of the tubeat the location at which molten metal is present in use.

According to a second aspect of the invention we provide processingapparatus for molten metal, the apparatus comprising a tube, the tubeleading to a location at which molten metal is provided in use, a gaspermeable element being provided between the end of the tube at thelocation at which molten metal is present in use.

Preferably the apparatus includes a chamber for the molten metal.Preferably the apparatus includes a molten metal mover. Preferably theapparatus includes an inlet leading from the chamber to the molten metalmover. Preferably the apparatus includes an outlet leading from themolten metal mover to the chamber. Preferably the tube leads into theapparatus at a location, the location being between 10 cm before thestart of the inlet and 10 cm after the end of the outlet, preferablybeing between the start of the inlet and the end of the inlet.

The tube preferably leads into the apparatus other than within themolten metal mover, particularly the part thereof which imparts motionto the molten metal. Preferably the tube leads into the apparatusbetween the end of the molten metal mover and the end of the outlet.

The tube may be provided in a component around the outlet The tubepreferably leads into the outlet at a location removed from the chargewell. The tube preferably leads into the apparatus at the beginning ofthe outlet. The tube preferably leads into the apparatus at the outletfrom the molten metal mover.

According to a third aspect of the invention we provide processingapparatus for introducing a gas to a volume of molten metal, theapparatus including a charge well into which solid metal to be melted isintroduced, an electromagnetic pump, an inlet leading from the chargewell to the pump, an outlet leading from the pump to the charge well, atube leading into the outlet from the pump, the tube leading into theoutlet at a location removed from the charge well.

Preferably the apparatus includes a furnace. Preferably the outlet formthe charge well leads to the furnace and the metal then passes on to thepump. Preferably the inlet to the charge well leads from the furnace,via the pump.

The tube may lead to a location at which molten metal is provided inuse, a gas permeable element being provided between the end of the tubeat the location at which molten metal is present in use.

According to a fourth aspect of the invention we provide processingapparatus for introducing solid metal to a volume of molten metal, theapparatus including a charge well into which solid metal to be melted isintroduced, an electromagnetic pump, an inlet leading from the chargewell to the pump and an outlet leading from the pump to the charge well,a tube leading into the outlet from the pump, the tube being provided ina wall of the charge well.

Preferably the apparatus includes a furnace, ideally separate from thecharge well. Preferably the outlet from the charge well leads to thefurnace. Preferably the inlet to the charge well leads from the furnace.

According to a fifth aspect of the invention we provide processingapparatus for molten metal, the apparatus including a chamber for themolten metal, a molten metal mover, an inlet leading from the chamber tothe molten metal mover and an outlet leading from the molten metal moverto the chamber, a conduit leading into the apparatus between the inletand the outlet, the conduit being provided with a gas permeable elementat its end, in contact with the inside of the chamber.

The aspects of the invention may include one or more of the followingfeatures, options or possibilities.

The metal may be aluminum. The solid metal may be scrap metal, forinstance used beverage cans.

The chamber, particularly a charge well, is refractory lined.

The electromagnetic pump preferably includes a through passage enclosedwithin one or more conducting coils. A silicon carbide passage ispreferred. Preferably a multilayered coil is provided. Preferably thepolarity across the coils can be reversed. Preferably the voltageapplied to the coils can be varied.

The inlet and/or outlet are preferably refractory lined. The inlet maylead directly to the chamber or charge well. The inlet may lead to thechamber or charge well via one or more other components, for instance anintervening chamber. The outlet may lead indirectly to the chamber orcharge well, but preferably leads there directly.

In one embodiment, the invention may particularly provide from thefollowing. The tube may be substantially vertically provided, forinstance within 5° of vertical. Preferably the tube is in contact withthe chamber/charge well along at least a part of its length. Preferablythe contact extends the entire length of the tube, at least below thelevel of the molten metal in use. Preferably the tube is received withinthe wall in a passage. Preferably the passage has an opening to thechamber/charge well along at least part of its length. Preferably theopening extends along the entire length of the passage, at least belowthe level of the molten metal in use. Preferably the passage is ofcircular cross-section with a portion cut away. The cut away portion ispreferably determined by the interception of the passage's circularcross-section with the chamber/charge well. Preferably the tube is ofcircular cross-section. Preferably the tube is a snug fit within thepassage. Preferably the tube is of metal. Preferably the end of the tubeis flush with the adjoining portion of the inlet or outlet Preferablythe end of the tube is flush with the adjoining portion of therefractory lining. Preferably the end of the tube is provided in theoutlet. Preferably the end of the tube is provided at the end of theoutlet nearest the chamber/charge well.

In another embodiment, the invention may particularly provide from thefollowing. The tube may be substantially vertically provided, forinstance within 5° of the vertical. Preferably the tube is separate fromthe chamber/charge well along its length. The tube may be providedwithin the refractory surround for the chamber/charge well. The tube maybe provided in a separate component, particularly one mounted on theinlet to the chamber and/or outlet from the molten metal mover.Preferably the tube is of circular cross-section. One or more tubes maybe provided. Preferably the tubes approach the inlet to the chamberand/or outlet from the molten metal mover tangentially. Preferably thetube is of metal and/or the material being introduced through a gaspermeable element provided on the end of a tube. The end of the tubecontacts or enters a gas permeable element, such as a porous block.

Where a gas permeable element is provided, the element is preferablypermeable to gas without being permeable to molten metal, particularlyaluminum. The element may be provided with a gas tight seal around oneor more surfaces. The seal may be provided by a part of the element or acomponent which surrounds those parts of the element. The elementpreferably has at least one surface leading into the apparatus. The oneor more surfaces may be configured to match one or more adjoining parts,for instance the adjoining parts of the outlet. The one or more surfacesare preferably flush with the surrounding parts of the outlet.

Preferably the tube is connected to a source of material to be added tothe molten metal. The source may be a pressurized source of a gas ormore than one gas. The source may be a source of solid material, forinstance one or more powders. The source may provide a mixture ofmaterials.

The method may particularly provide that gas leaves the gas permeableelement and enters the molten metal, without molten metal entering thegas permeable element.

Preferably the gas reacts with the metal or one or more constituentparts thereof, for instance magnesium in aluminum. Preferably thereaction has completed before the gas reaches the end of the outletand/or enters the chamber. Preferably the gas is not longer present asbubbles by the time it reaches the end of the outlet and/or enters thechamber. Preferably the gas flow rate into the outlet and/or thedistance between the location at which gas enters the outlet and the endof the outlet are controlled so as to ensure the reaction is completedand/or no gas is left and/or no gas bubbles are left.

Particularly in another embodiment, the invention may particularlyprovide from the following. The gas permeable element may be provided inthe side wall. The element may be a truncated cone. The element may havea porosity of between 5 and 20%, more preferably 12%+/−2%. One or moretubes may be provided in the element. The tubes may be connected to achamber supplied with gas. Three tubes may be provided. The tubes may befilled apart from a series of slots. Four slots may be provided. Theslots may be parallel to one another. The element may be provided in theside wall adjacent the outlet, for instance within 20 degrees of thestart thereof. The element may be provided in the part of the chamberwall followed by the metal as it moves from the inlet towards theoutlet. Preferably the element is provided within 10% of the sameheight, and ideally at the same height, as the outlet.

According to a fifth aspect of the invention we provide a method ofintroducing material into a molten metal, the method including providingapparatus including a chamber, providing molten metal within the chamberand circulating the molten metal through an outlet from the chamber to amolten metal mover and from the molten metal mover through an outlet tothe chamber, the material being introduced through a tube which entersthe apparatus between the start of the inlet and the end of the outlet.

The material may be introduced as a solid. The material may beintroduced as a gas. The material may include one or more materials. Thematerial may include one or more solids and one or more gases. Differentmaterials may be introduced at different times. The material may beintroduced to remove a component of the molten metal. The material maybe introduced to add a component to the molten metal.

Various embodiments of the invention will now be described, by way ofexample only, in which:

FIG. 1 illustrates a charge well and electromagnetic pump according toone embodiment of the invention;

FIG. 2 illustrates a plan view of the charge well showing the materialcharging tube;

FIG. 3 illustrates a partial sectioned side view showing theinterrelationship between the end of the material charging tube and thepump outlet;

FIG. 4 illustrates a cross-section through a pump outlet and end sectionof a material charging tube according to another embodiment of theinvention; and

FIG. 5 illustrates a partial sectioned side view showing theinterrelationship between the material charging tube and the pumpoutlet.

FIG. 1 illustrates one possible embodiment of the invention, in thiscase in relation to solid metal melting apparatus. The apparatusincludes a charge well 1 into which solid metal 3 is introduced so as tointimately contact it with and melt it into molten metal 5. The chargewell 1 has an internal profile which in combination with rapid moltenmetal flow causes a vortex on the molten metal surface which promotesthe blending of the solid metal 3 into the molten metal 5 rapidly andefficiently. The rapid molten metal flow is generated by anelectromagnetic pump unit 7 which causes molten metal 5 to leave thecharge well 1 via exit 9 pass along pipe 11 through the furnace, notshown, and back to pump unit 7 along pipe 12 and then back to the chargewell 1 along pipe 13 to inlet 15. Electromagnetic pumps work on thelinear motor principal in which a conductor is magnetically repulsed bya magnetic field generated by the surrounding coil. The pipe 13 isaligned with the charge well 1 in a substantially tangential manner topromote the vortex formation in the charge well 1. Further details ofthe design, its principals and operation are to be found in GB-B-2269889the contents of which, particularly in relation to features of thecharge well configuration, electromagnetic pump principles and operationand system configuration, are incorporated herein by reference.

This embodiment represents just one situation in which the presentinvention might be used, other possibilities include molten metalcirculation systems, furnaces or other solid metal charginginstallations where metal flow occurs.

Whilst the configuration described above is useful for introducing solidmetal 3 into the molten metal 5 merely introducing a substance to themolten metal surface is not sufficient in the case of lighter materialsor materials in finer form. If powders are introduced to the surfacethen a significant proportion thereof will remain on the surface and notcontact the molten metal 5. The problem is clearly greater still if thematerial to be added is a gas.

To introduce gases into molten metal lances are frequently used in theprior art. These are hollow tubes formed of refractory material whichare maneuvered over the molten metal and dipped in when it is desired toadd material. The material, gaseous, is then blown down the lance andinto the molten metal. A significant portion of the gas escapes straightto the surface and its function is lost as a result There are alsolimits on the rate of gas introduction, as too high a gas flow rateleads to substantial bubbles forming in the molten metal which isundesirable. As a consequence gas introduction using lances is timeconsuming and relatively wasteful. There are also safety issues wherefor instance the material being introduced is hazardous, for instancechlorine.

The embodiment of the invention illustrated in FIG. 1 involves amaterial charging tube 20 which is fed material X from a feeder 22.Where the material is solid then a separate gas feeder 24 may beprovided to assist the charging of the material into and along tube 20or act as a supply of alternative material Y.

As can be seen in the plan view of FIG. 2, the material charging tube 22is retained within a passage 26 in the refractory lining 28 of thecharge well 1. The passage 26 is open to the inside 30 of the chargewell 1, and as a consequence molten metal 5 contacts the outside of thetube 22 in use. The passage 26 encloses the tube 22 to a sufficientextent, however, to fully retain it in position; the gap 32 is of lesserdimension than the diameter D of the tube 22. The contact between themolten metal 5 and the tube 22 means that the tube is kept hot in useand this avoids any problems with the material X holding up in the tube22 or molten metal 5 siphoning out of the charge well 1.

To maximise the contact between the material X and the molten metal 5the end 34 of the tube 22 is positioned in the part 36 of the refractorylining 28 which leads from the outlet pipe 11 into the charge well 1. Atthis point the molten metal has a very high flow rate as the moltenmetal 5 is passing through a limited cross-section and the pump unit 7outputs a significant flow. As the material X leaves the end 34 of thetube 22 it is quickly swept by the molten metal 5 away from the end 34and into the molten metal 5. The turbulent flow characteristics and highspeed of the molten metal mean that the material X is quickly and widelydistributed within the molten metal 5 as a whole. Additionally as thematerial X is introduced a long way from the molten metal surface in thecharge well take up of the material X by the time any of it reaches thesurface is almost total (92% compared with 40 to 50% from lances). Dueto the flow rate present high flow rates of material X into the moltenmetal 5 can also be provided with out risk of large bubble formation(300% the flow rate of lances).

The material X, particularly in the case of gaseous material, isdesirably added at the exit from the pump unit 7, rather than at theinlet, so as to avoid the presence of gas voids within the pump unit 7which impairs its pumping capacity. Solid materials, could be introducedinto the inlet, where the flow rate is also high, without such problems,if desired.

The passage 26 can be drilled into existing refractory linings 28 toallow retro-fitting of the invention if desired. Alternatively therefractory ling 28 can be produced with the passage 26 present from thestart. The tube 22 is inserted from above.

The invention is suitable for use in introducing a wide variety ofmaterials into the molten metal, including but not limited to: chlorine,nitrogen, alloying materials (metal and/or non-metal), fluxes, silicon,etc.

The materials can be introduced individually or in combinations. Forinstance, nitrogen gas can be used to convey a powder into the moltenmetal whilst also providing the purifying action of nitrogen at the sametime. Different materials may be added at different times using theinvention, for instance chlorine followed by nitrogen etc.

An embodiment of the invention, particularly suited to the introductionof gases only, is shown in FIGS. 4 and 5. Such an embodiment isparticularly suited to introducing chlorine into molten aluminum toremove magnesium, for instance.

The gas 40 to be introduced is fed down a material charging tube 42. Asingle tube or multiple tubes may be used. The tube 42 is surrounded byrefractory material 44 and ends at porous block 46. The porous block 46is surrounded by refractory material 44 to provide a gas tight sealaround it, other than where the porous block 46 is exposed at surface 48to the inside of the outlet pipe 50 which returns the molten metal fromthe pump, not shown. the porous block 46 occupies a position around partof the side of the outlet pipe 50 and hence the gas flowing through theporous block 46 and into the outlet pipe 50 tends to enter the outletpipe tangentially.

The porous material is designed to have small pores. As a result, smallgas bubbles are formed at its surface and are chopped into the moltenmetal by the metals flow past the surface of the porous block These thendisperse quickly in the metal. Furthermore, the small size of thebubbles means that they have a higher surface area to volume ratio andso react quicker with the metal or constituents of it.

The porous material block is such that even when gas pressure isremoved, no molten metal flows into the porous block. As a consequence,there is no risk of molten metal cooling in the porous block andsolidifying there. The problem with molten metal syphoning up thematerial charging tube is also avoided. Because no metal ever enters thematerial charging tube there is no need to keep the tube hot This allowsit to be positioned in a variety of locations. It is believed that aslow decrease in the gas pressure causes a very small amount of metal toenter the skin of the block and freeze there. When a high gas pressureis applied at the start of the next gas phase then this metal is blownout and gas flow recommences.

The porous material block may have an apparent porosity of around 12%,density of around 3.06 g/cm3. It may be an alumina spinel.

In one advantageous position, as shown in FIG. 4, the material chargingtube is provided at the outlet from the pump unit, with the length ofthe return pipe between there and the charge well, furnace or otherlarge volume of metal. As a result of this position it is possible toset the gas flow so that the reaction between the gas and the metal hascompleted before the metal leaves the confines of the return pipe. Thishas the advantage of eliminating gas loss out of the metal by bubblesreaching the surface. Positioning the material charging tube at thisposition still has the benefits of the gas being introduced at a highflow location, due to the relative constriction of the return pipe,which gives turbulent conditions and leads to quick and widespreadmixing of the gas with the metal. The gas still does not impair thepumping function because gas voids in the pump itself are avoided.

An still further alternative is shown in FIG. 6 in terms of a porousmaterial block 100 which is mounted in the side wall 102 of a chargewell 104 or the like. Molten metal is pumped into the charge wellthrough inlet 106 and leaves through outlet 108. This action causes avortex to form in the charge well. Gas entering through the porousmaterial block 100 enters the metal and is at least in part swept intothe outlet and on into the furnace. By the time the metal returns to theopen charge well it has fully dissolved.

More detail of the porous material block 100 is shown in FIG. 6. A feedtube 110 connects to a void 112 which in turn feeds gas to three tubes114 (only one of which is shown). The tubes 114 have a series oflongitudinally extending slits in them. The slits are sized according tothe gas bubble size desired, but generally ensure small and hencequickly dissolved bubbles. The tubes 114 are evenly dispersed within thealumina spinal material 116.

1. Processing apparatus for molten metal, the apparatus including achamber for the molten metal, a molten metal mover, an inlet leadingfrom the chamber to the molten metal mover and an outlet leading fromthe molten metal mover to the chamber, a tube leading into the apparatusbetween the start of the inlet and the end of the outlet.
 2. Processingapparatus for molten metal, preferably according to claim 1, theapparatus comprising a tube, the tube leading to a location at whichmolten metal is provided in use, a gas permeable element being providedbetween the end of the tube at the location at which molten metal ispresent in use.
 3. Processing apparatus according to claim 1 forintroducing a gas to a volume of molten metal, the apparatus including acharge well into which solid metal to be melted is introduced, anelectromagnetic pump, an inlet leading from the charge well to the pump,an outlet leading from the pump to the charge well, a tube leading intothe outlet from the pump, the tube leading into the outlet at a locationremoved from the charge well.
 4. Processing apparatus according to claim3 in which the outlet form the charge well leads to the furnace and themetal then passes on to the pump.
 5. Processing apparatus according toclaim 1 for introducing solid metal to a volume of molten metal, theapparatus including a charge well into which solid metal to be melted isintroduced, an electromagnetic pump, an inlet leading from the chargewell to the pump and an outlet leading from the pump to the charge well,a tube leading into the outlet from the pump, the tube being provided ina wall of the charge well.
 6. Processing apparatus according to claim 5in which the outlet from the charge well leads to the furnace. 7.Processing apparatus according to claim 1 for melting metal or metalcontaining materials and/or for processing molten metal and/or forpurifying molten metal and/or for distributing molten metal. 8.Processing apparatus according to claim 1 in which the tube leads intothe apparatus between the end of the molten metal mover and the end ofthe outlet.
 9. Processing apparatus according to claim 1 in which thetube is in contact with the chamber/charge well along at least a part ofits length.
 10. Processing apparatus according to claim 9 in which thetube is received within the wall of the chamber/charge well in a passageand the passage has an opening to the chamber/charge well along at leastpart of its length.
 11. Processing apparatus according to claim 9 inwhich the passage is of circular cross-section with a portion cut away.12. Processing apparatus according to claim 2 in which the gas permeableelement is permeable to gas without being permeable to molten metal. 13.Processing apparatus according claim 1 in which the tube is connected toa source of material to be added to the molten metal.
 14. Processingapparatus according to claim 2 the element having a porosity of between5 and 20%.
 15. A method of introducing material into a molten metal, themethod including providing apparatus including a chamber, providingmolten metal within the chamber and circulating the molten metal throughan outlet from the chamber to a molten metal mover and from the moltenmetal mover through an outlet to the chamber, the material beingintroduced through a tube which enters the apparatus between the startof the inlet and the end of the outlet.
 16. A method according to claim15 in which the method provides that gas leaves the tube through a gaspermeable element and enters the molten metal, without molten metalentering the gas permeable element.
 17. A method according to claim 15in which the gas reacts with the metal or one or more constituent partsthereof and the reaction has completed before the gas reaches the end ofthe outlet and/or enters the chamber.
 18. A method according to claim 15in which the gas flow rate into the outlet and/or the distance betweenthe location at which gas enters the outlet and the end of the outletare controlled so as to ensure the reaction is completed and/or no gasis left and/or no gas bubbles are left by the time the molten metalleaves the outlet.
 19. A method according to claim 15 in which thematerial is introduced as a solid.